1. Department of Energy and Materials Engineering and Advanced Energy and Electronic Materials Research Center (AEEMRC), Dongguk University—Seoul, Seoul 100-715, Republic of Korea
2. Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea
3. Departments of Energy Science and Physics, Sungkyunkwan University, Suwon 440-746, Republic of Korea
4. Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST), Jeollabuk-Do 565-902, Republic of Korea
5. Department of Physics, Dongguk University—Seoul, Seoul 100-715, Republic of Korea
6. Department of Electrical Engineering and Computer Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States